/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
- Copyright (C) 2008-2013 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2008-2014 Marco Costalba, Joona Kiiski, Tord Romstad
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
double BestMoveChanges;
Value DrawValue[COLOR_NB];
HistoryStats History;
+ GainsStats Gains;
CountermovesStats Countermoves;
template <NodeType NT>
void id_loop(Position& pos);
Value value_to_tt(Value v, int ply);
Value value_from_tt(Value v, int ply);
- bool allows(const Position& pos, Move first, Move second);
- bool refutes(const Position& pos, Move first, Move second);
string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
struct Skill {
<< std::endl;
}
- // Reset the threads, still sleeping: will be wake up at split time
+ // Reset the threads, still sleeping: will wake up at split time
for (size_t i = 0; i < Threads.size(); ++i)
Threads[i]->maxPly = 0;
sync_cout << "info nodes " << RootPos.nodes_searched()
<< " time " << Time::now() - SearchTime + 1 << sync_endl;
- // When we reach max depth we arrive here even without Signals.stop is raised,
- // but if we are pondering or in infinite search, according to UCI protocol,
- // we shouldn't print the best move before the GUI sends a "stop" or "ponderhit"
- // command. We simply wait here until GUI sends one of those commands (that
- // raise Signals.stop).
+ // When we reach the maximum depth, we can arrive here without a raise of
+ // Signals.stop. However, if we are pondering or in an infinite search,
+ // the UCI protocol states that we shouldn't print the best move before the
+ // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
+ // until the GUI sends one of those commands (which also raises Signals.stop).
if (!Signals.stop && (Limits.ponder || Limits.infinite))
{
Signals.stopOnPonderhit = true;
Value bestValue, alpha, beta, delta;
std::memset(ss-2, 0, 5 * sizeof(Stack));
+ (ss-1)->currentMove = MOVE_NULL; // Hack to skip update gains
depth = 0;
BestMoveChanges = 0;
TT.new_search();
History.clear();
+ Gains.clear();
Countermoves.clear();
PVSize = Options["MultiPV"];
// Age out PV variability metric
BestMoveChanges *= 0.8;
- // Save last iteration's scores before first PV line is searched and all
- // the move scores but the (new) PV are set to -VALUE_INFINITE.
+ // Save the last iteration's scores before first PV line is searched and
+ // all the move scores except the (new) PV are set to -VALUE_INFINITE.
for (size_t i = 0; i < RootMoves.size(); ++i)
RootMoves[i].prevScore = RootMoves[i].score;
beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
}
- // Start with a small aspiration window and, in case of fail high/low,
- // research with bigger window until not failing high/low anymore.
+ // Start with a small aspiration window and, in the case of a fail
+ // high/low, re-search with a bigger window until we're not failing
+ // high/low anymore.
while (true)
{
bestValue = search<Root>(pos, ss, alpha, beta, depth * ONE_PLY, false);
- // Bring to front the best move. It is critical that sorting is
- // done with a stable algorithm because all the values but the first
- // and eventually the new best one are set to -VALUE_INFINITE and
- // we want to keep the same order for all the moves but the new
- // PV that goes to the front. Note that in case of MultiPV search
- // the already searched PV lines are preserved.
+ // Bring the best move to the front. It is critical that sorting
+ // is done with a stable algorithm because all the values but the
+ // first and eventually the new best one are set to -VALUE_INFINITE
+ // and we want to keep the same order for all the moves except the
+ // new PV that goes to the front. Note that in case of MultiPV
+ // search the already searched PV lines are preserved.
std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
// Write PV back to transposition table in case the relevant
RootMoves[i].insert_pv_in_tt(pos);
// If search has been stopped break immediately. Sorting and
- // writing PV back to TT is safe becuase RootMoves is still
- // valid, although refers to previous iteration.
+ // writing PV back to TT is safe because RootMoves is still
+ // valid, although it refers to previous iteration.
if (Signals.stop)
break;
// When failing high/low give some update (without cluttering
- // the UI) before to research.
+ // the UI) before a re-search.
if ( (bestValue <= alpha || bestValue >= beta)
&& Time::now() - SearchTime > 3000)
sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
// In case of failing low/high increase aspiration window and
- // research, otherwise exit the loop.
+ // re-search, otherwise exit the loop.
if (bestValue <= alpha)
{
alpha = std::max(bestValue - delta, -VALUE_INFINITE);
sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
}
- // Do we need to pick now the sub-optimal best move ?
+ // If skill levels are enabled and time is up, pick a sub-optimal best move
if (skill.enabled() && skill.time_to_pick(depth))
skill.pick_move();
<< std::endl;
}
- // Do we have found a "mate in x"?
+ // Have we found a "mate in x"?
if ( Limits.mate
&& bestValue >= VALUE_MATE_IN_MAX_PLY
&& VALUE_MATE - bestValue <= 2 * Limits.mate)
{
bool stop = false; // Local variable, not the volatile Signals.stop
- // Take in account some extra time if the best move has changed
+ // Take some extra time if the best move has changed
if (depth > 4 && depth < 50 && PVSize == 1)
TimeMgr.pv_instability(BestMoveChanges);
- // Stop search if most of available time is already consumed. We
+ // Stop the search if most of the available time has been used. We
// probably don't have enough time to search the first move at the
// next iteration anyway.
if (Time::now() - SearchTime > (TimeMgr.available_time() * 62) / 100)
stop = true;
- // Stop search early if one move seems to be much better than others
+ // Stop the search early if one move seems to be much better than others
if ( depth >= 12
&& BestMoveChanges <= DBL_EPSILON
&& !stop
if (stop)
{
// If we are allowed to ponder do not stop the search now but
- // keep pondering until GUI sends "ponderhit" or "stop".
+ // keep pondering until the GUI sends "ponderhit" or "stop".
if (Limits.ponder)
Signals.stopOnPonderhit = true;
else
// search<>() is the main search function for both PV and non-PV nodes and for
// normal and SplitPoint nodes. When called just after a split point the search
// is simpler because we have already probed the hash table, done a null move
- // search, and searched the first move before splitting, we don't have to repeat
- // all this work again. We also don't need to store anything to the hash table
- // here: This is taken care of after we return from the split point.
+ // search, and searched the first move before splitting, so we don't have to
+ // repeat all this work again. We also don't need to store anything to the hash
+ // table here: This is taken care of after we return from the split point.
template <NodeType NT>
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
const TTEntry *tte;
SplitPoint* splitPoint;
Key posKey;
- Move ttMove, move, excludedMove, bestMove, threatMove;
- Depth ext, newDepth;
- Value bestValue, value, ttValue;
- Value eval, nullValue;
+ Move ttMove, move, excludedMove, bestMove;
+ Depth ext, newDepth, predictedDepth;
+ Value bestValue, value, ttValue, eval, nullValue, futilityValue;
bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
bool captureOrPromotion, dangerous, doFullDepthSearch;
int moveCount, quietCount;
{
splitPoint = ss->splitPoint;
bestMove = splitPoint->bestMove;
- threatMove = splitPoint->threatMove;
bestValue = splitPoint->bestValue;
tte = NULL;
ttMove = excludedMove = MOVE_NONE;
moveCount = quietCount = 0;
bestValue = -VALUE_INFINITE;
- ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
+ ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
ss->ply = (ss-1)->ply + 1;
(ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
(ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
// Step 3. Mate distance pruning. Even if we mate at the next move our score
// would be at best mate_in(ss->ply+1), but if alpha is already bigger because
// a shorter mate was found upward in the tree then there is no need to search
- // further, we will never beat current alpha. Same logic but with reversed signs
- // applies also in the opposite condition of being mated instead of giving mate,
- // in this case return a fail-high score.
+ // because we will never beat the current alpha. Same logic but with reversed
+ // signs applies also in the opposite condition of being mated instead of giving
+ // mate. In this case return a fail-high score.
alpha = std::max(mated_in(ss->ply), alpha);
beta = std::min(mate_in(ss->ply+1), beta);
if (alpha >= beta)
ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
- // At PV nodes we check for exact scores, while at non-PV nodes we check for
- // a fail high/low. Biggest advantage at probing at PV nodes is to have a
+ // At PV nodes we check for exact scores, whilst at non-PV nodes we check for
+ // a fail high/low. The biggest advantage to probing at PV nodes is to have a
// smooth experience in analysis mode. We don't probe at Root nodes otherwise
// we should also update RootMoveList to avoid bogus output.
if ( !RootNode
TT.refresh(tte);
ss->currentMove = ttMove; // Can be MOVE_NONE
+ // Update killers, history, and counter move on TT hit
if ( ttValue >= beta
&& ttMove
&& !pos.capture_or_promotion(ttMove)
- && ttMove != ss->killers[0])
+ && !inCheck)
{
- ss->killers[1] = ss->killers[0];
- ss->killers[0] = ttMove;
+ if (ss->killers[0] != ttMove)
+ {
+ ss->killers[1] = ss->killers[0];
+ ss->killers[0] = ttMove;
+ }
+
+ Value bonus = Value(int(depth) * int(depth));
+ History.update(pos.moved_piece(ttMove), to_sq(ttMove), bonus);
+
+ if (is_ok((ss-1)->currentMove))
+ {
+ Square prevMoveSq = to_sq((ss-1)->currentMove);
+ Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, ttMove);
+ }
}
return ttValue;
}
TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
}
+ if ( !pos.captured_piece_type()
+ && ss->staticEval != VALUE_NONE
+ && (ss-1)->staticEval != VALUE_NONE
+ && (move = (ss-1)->currentMove) != MOVE_NULL
+ && type_of(move) == NORMAL)
+ {
+ Square to = to_sq(move);
+ Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
+ }
+
// Step 6. Razoring (skipped when in check)
if ( !PvNode
&& depth < 4 * ONE_PLY
Value v = qsearch<NonPV, false>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
if (v < rbeta)
// Logically we should return (v + razor_margin(depth)), but
- // surprisingly this did slightly weaker in tests.
+ // surprisingly this performed slightly weaker in tests.
return v;
}
if (v >= beta)
return nullValue;
}
- else
- {
- // The null move failed low, which means that we may be faced with
- // some kind of threat. If the previous move was reduced, check if
- // the move that refuted the null move was somehow connected to the
- // move which was reduced. If a connection is found, return a fail
- // low score (which will cause the reduced move to fail high in the
- // parent node, which will trigger a re-search with full depth).
- threatMove = (ss+1)->currentMove;
-
- if ( depth < 5 * ONE_PLY
- && (ss-1)->reduction
- && threatMove != MOVE_NONE
- && allows(pos, (ss-1)->currentMove, threatMove))
- return alpha;
- }
}
// Step 9. ProbCut (skipped when in check)
continue;
// At root obey the "searchmoves" option and skip moves not listed in Root
- // Move List, as a consequence any illegal move is also skipped. In MultiPV
+ // Move List. As a consequence any illegal move is also skipped. In MultiPV
// mode we also skip PV moves which have been already searched.
if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
continue;
if (SpNode)
{
- // Shared counter cannot be decremented later if move turns out to be illegal
+ // Shared counter cannot be decremented later if the move turns out to be illegal
if (!pos.legal(move, ci.pinned))
continue;
captureOrPromotion = pos.capture_or_promotion(move);
givesCheck = pos.gives_check(move, ci);
dangerous = givesCheck
- || pos.passed_pawn_push(move)
- || type_of(move) == CASTLE;
+ || type_of(move) != NORMAL
+ || pos.advanced_pawn_push(move);
// Step 12. Extend checks
if (givesCheck && pos.see_sign(move) >= 0)
// Singular extension search. If all moves but one fail low on a search of
// (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
// is singular and should be extended. To verify this we do a reduced search
- // on all the other moves but the ttMove, if result is lower than ttValue minus
- // a margin then we extend ttMove.
+ // on all the other moves but the ttMove and if the result is lower than
+ // ttValue minus a margin then we extend the ttMove.
if ( singularExtensionNode
&& move == ttMove
&& !ext
ext = ONE_PLY;
}
- // Update current move (this must be done after singular extension search)
+ // Update the current move (this must be done after singular extension search)
newDepth = depth - ONE_PLY + ext;
// Step 13. Pruning at shallow depth (exclude PV nodes)
{
// Move count based pruning
if ( depth < 16 * ONE_PLY
- && moveCount >= FutilityMoveCounts[improving][depth]
- && (!threatMove || !refutes(pos, move, threatMove)))
+ && moveCount >= FutilityMoveCounts[improving][depth] )
{
if (SpNode)
splitPoint->mutex.lock();
continue;
}
-
Depth predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
+ predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
// Futility pruning: parent node
if (predictedDepth < 7 * ONE_PLY)
{
- Value futilityValue = ss->staticEval + futility_margin(predictedDepth) + Value(128);
+ futilityValue = ss->staticEval + futility_margin(predictedDepth)
+ + Value(128) + Gains[pos.moved_piece(move)][to_sq(move)];
if (futilityValue <= alpha)
{
}
// Prune moves with negative SEE at low depths
- if ( predictedDepth < 4 * ONE_PLY
- && pos.see_sign(move) < 0)
+ if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < 0)
{
if (SpNode)
splitPoint->mutex.lock();
continue;
}
-
}
- // Check for legality only before to do the move
+ // Check for legality just before making the move
if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
{
- --moveCount;
+ moveCount--;
continue;
}
// Step 14. Make the move
pos.do_move(move, st, ci, givesCheck);
- // Step 15. Reduced depth search (LMR). If the move fails high will be
+ // Step 15. Reduced depth search (LMR). If the move fails high it will be
// re-searched at full depth.
if ( depth >= 3 * ONE_PLY
&& !pvMove
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
+ // Research at intermediate depth if reduction is very high
+ if (value > alpha && ss->reduction >= 4 * ONE_PLY)
+ {
+ Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
+ value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d2, true);
+ }
+
doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
ss->reduction = DEPTH_ZERO;
}
: - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
}
- // Only for PV nodes do a full PV search on the first move or after a fail
- // high, in the latter case search only if value < beta, otherwise let the
- // parent node to fail low with value <= alpha and to try another move.
+ // For PV nodes only, do a full PV search on the first move or after a fail
+ // high (in the latter case search only if value < beta), otherwise let the
+ // parent node fail low with value <= alpha and to try another move.
if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
value = newDepth < ONE_PLY ?
givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
++BestMoveChanges;
}
else
- // All other moves but the PV are set to the lowest value, this
- // is not a problem when sorting becuase sort is stable and move
- // position in the list is preserved, just the PV is pushed up.
+ // All other moves but the PV are set to the lowest value: this is
+ // not a problem when sorting because the sort is stable and the
+ // move position in the list is preserved - just the PV is pushed up.
rm.score = -VALUE_INFINITE;
}
assert(bestValue < beta);
thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
- depth, threatMove, moveCount, &mp, NT, cutNode);
+ depth, moveCount, &mp, NT, cutNode);
if (bestValue >= beta)
break;
}
// case of Signals.stop or thread.cutoff_occurred() are set, but this is
// harmless because return value is discarded anyhow in the parent nodes.
// If we are in a singular extension search then return a fail low score.
- // A split node has at least one move, the one tried before to be splitted.
+ // A split node has at least one move - the one tried before to be splitted.
if (!moveCount)
return excludedMove ? alpha
: inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
ss->currentMove = bestMove = MOVE_NONE;
ss->ply = (ss-1)->ply + 1;
- // Check for an instant draw or maximum ply reached
+ // Check for an instant draw or if the maximum ply has been reached
if (pos.is_draw() || ss->ply > MAX_PLY)
return DrawValue[pos.side_to_move()];
- // Decide whether or not to include checks, this fixes also the type of
+ // Decide whether or not to include checks: this fixes also the type of
// TT entry depth that we are going to use. Note that in qsearch we use
// only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
&& !InCheck
&& !givesCheck
&& move != ttMove
- && type_of(move) != PROMOTION
&& futilityBase > -VALUE_KNOWN_WIN
- && !pos.passed_pawn_push(move))
+ && !pos.advanced_pawn_push(move))
{
- futilityValue = futilityBase
- + PieceValue[EG][pos.piece_on(to_sq(move))]
- + (type_of(move) == ENPASSANT ? PawnValueEg : VALUE_ZERO);
+ assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
+
+ futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
if (futilityValue < beta)
{
continue;
}
- // Prune moves with negative or equal SEE and also moves with positive
- // SEE where capturing piece loses a tempo and SEE < beta - futilityBase.
- if ( futilityBase < beta
- && pos.see(move, beta - futilityBase) <= 0)
+ if (futilityBase < beta && pos.see(move) <= 0)
{
bestValue = std::max(bestValue, futilityBase);
continue;
}
}
- // Detect non-capture evasions that are candidate to be pruned
+ // Detect non-capture evasions that are candidates to be pruned
evasionPrunable = InCheck
&& bestValue > VALUE_MATED_IN_MAX_PLY
&& !pos.capture(move)
&& pos.see_sign(move) < 0)
continue;
- // Check for legality only before to do the move
+ // Check for legality just before making the move
if (!pos.legal(move, ci.pinned))
continue;
// value_to_tt() adjusts a mate score from "plies to mate from the root" to
// "plies to mate from the current position". Non-mate scores are unchanged.
- // The function is called before storing a value to the transposition table.
+ // The function is called before storing a value in the transposition table.
Value value_to_tt(Value v, int ply) {
// value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
- // from the transposition table (where refers to the plies to mate/be mated
+ // from the transposition table (which refers to the plies to mate/be mated
// from current position) to "plies to mate/be mated from the root".
Value value_from_tt(Value v, int ply) {
}
- // allows() tests whether the 'first' move at previous ply somehow makes the
- // 'second' move possible, for instance if the moving piece is the same in
- // both moves. Normally the second move is the threat (the best move returned
- // from a null search that fails low).
-
- bool allows(const Position& pos, Move first, Move second) {
-
- assert(is_ok(first));
- assert(is_ok(second));
- assert(color_of(pos.piece_on(from_sq(second))) == ~pos.side_to_move());
- assert(type_of(first) == CASTLE || color_of(pos.piece_on(to_sq(first))) == ~pos.side_to_move());
-
- Square m1from = from_sq(first);
- Square m2from = from_sq(second);
- Square m1to = to_sq(first);
- Square m2to = to_sq(second);
-
- // The piece is the same or second's destination was vacated by the first move
- // We exclude the trivial case where a sliding piece does in two moves what
- // it could do in one move: eg. Ra1a2, Ra2a3.
- if ( m2to == m1from
- || (m1to == m2from && !squares_aligned(m1from, m2from, m2to)))
- return true;
-
- // Second one moves through the square vacated by first one
- if (between_bb(m2from, m2to) & m1from)
- return true;
-
- // Second's destination is defended by the first move's piece
- Bitboard m1att = pos.attacks_from(pos.piece_on(m1to), m1to, pos.pieces() ^ m2from);
- if (m1att & m2to)
- return true;
-
- // Second move gives a discovered check through the first's checking piece
- if (m1att & pos.king_square(pos.side_to_move()))
- {
- assert(between_bb(m1to, pos.king_square(pos.side_to_move())) & m2from);
- return true;
- }
-
- return false;
- }
-
-
- // refutes() tests whether a 'first' move is able to defend against a 'second'
- // opponent's move. In this case will not be pruned. Normally the second move
- // is the threat (the best move returned from a null search that fails low).
-
- bool refutes(const Position& pos, Move first, Move second) {
-
- assert(is_ok(first));
- assert(is_ok(second));
-
- Square m1from = from_sq(first);
- Square m2from = from_sq(second);
- Square m1to = to_sq(first);
- Square m2to = to_sq(second);
-
- // Don't prune moves of the threatened piece
- if (m1from == m2to)
- return true;
-
- // If the threatened piece has value less than or equal to the value of the
- // threat piece, don't prune moves which defend it.
- if ( pos.capture(second)
- && ( PieceValue[MG][pos.piece_on(m2from)] >= PieceValue[MG][pos.piece_on(m2to)]
- || type_of(pos.piece_on(m2from)) == KING))
- {
- // Update occupancy as if the piece and the threat are moving
- Bitboard occ = pos.pieces() ^ m1from ^ m1to ^ m2from;
- Piece pc = pos.piece_on(m1from);
-
- // The moved piece attacks the square 'tto' ?
- if (pos.attacks_from(pc, m1to, occ) & m2to)
- return true;
-
- // Scan for possible X-ray attackers behind the moved piece
- Bitboard xray = (attacks_bb< ROOK>(m2to, occ) & pos.pieces(color_of(pc), QUEEN, ROOK))
- | (attacks_bb<BISHOP>(m2to, occ) & pos.pieces(color_of(pc), QUEEN, BISHOP));
-
- // Verify attackers are triggered by our move and not already existing
- if (unlikely(xray) && (xray & ~pos.attacks_from<QUEEN>(m2to)))
- return true;
- }
-
- // Don't prune safe moves which block the threat path
- if ((between_bb(m2from, m2to) & m1to) && pos.see_sign(first) >= 0)
- return true;
-
- return false;
- }
-
-
- // When playing with strength handicap choose best move among the MultiPV set
- // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
+ // When playing with a strength handicap, choose best move among the MultiPV
+ // set using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
Move Skill::pick_move() {
best = MOVE_NONE;
// Choose best move. For each move score we add two terms both dependent on
- // weakness, one deterministic and bigger for weaker moves, and one random,
+ // weakness. One deterministic and bigger for weaker moves, and one random,
// then we choose the move with the resulting highest score.
for (size_t i = 0; i < PVSize; ++i)
{
}
- // uci_pv() formats PV information according to UCI protocol. UCI requires
- // to send all the PV lines also if are still to be searched and so refer to
- // the previous search score.
+ // uci_pv() formats PV information according to the UCI protocol. UCI
+ // requires that all (if any) unsearched PV lines are sent using a previous
+ // search score.
string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
/// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
-/// We consider also failing high nodes and not only BOUND_EXACT nodes so to
-/// allow to always have a ponder move even when we fail high at root, and a
-/// long PV to print that is important for position analysis.
+/// We also consider both failing high nodes and BOUND_EXACT nodes here to
+/// ensure that we have a ponder move even when we fail high at root. This
+/// results in a long PV to print that is important for position analysis.
void RootMove::extract_pv_from_tt(Position& pos) {
void Thread::idle_loop() {
// Pointer 'this_sp' is not null only if we are called from split(), and not
- // at the thread creation. So it means we are the split point's master.
+ // at the thread creation. This means we are the split point's master.
SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
assert(!this_sp || (this_sp->masterThread == this && searching));
break;
}
- // Do sleep after retesting sleep conditions under lock protection, in
+ // Do sleep after retesting sleep conditions under lock protection. In
// particular we need to avoid a deadlock in case a master thread has,
// in the meanwhile, allocated us and sent the notify_one() call before
// we had the chance to grab the lock.
sp->slavesMask &= ~(1ULL << idx);
sp->nodes += pos.nodes_searched();
- // Wake up master thread so to allow it to return from the idle loop
- // in case we are the last slave of the split point.
+ // Wake up the master thread so to allow it to return from the idle
+ // loop in case we are the last slave of the split point.
if ( Threads.sleepWhileIdle
&& this != sp->masterThread
&& !sp->slavesMask)
sp->masterThread->notify_one();
}
- // After releasing the lock we cannot access anymore any SplitPoint
- // related data in a safe way becuase it could have been released under
- // our feet by the sp master. Also accessing other Thread objects is
- // unsafe because if we are exiting there is a chance are already freed.
+ // After releasing the lock we can't access any SplitPoint related data
+ // in a safe way because it could have been released under our feet by
+ // the sp master. Also accessing other Thread objects is unsafe because
+ // if we are exiting there is a chance that they are already freed.
sp->mutex.unlock();
}
/// check_time() is called by the timer thread when the timer triggers. It is
-/// used to print debug info and, more important, to detect when we are out of
-/// available time and so stop the search.
+/// used to print debug info and, more importantly, to detect when we are out of
+/// available time and thus stop the search.
void check_time() {
projects / stockfish / blobdiff